The present invention generally relates to communication signal receivers, and particularly relates to automatic gain control in the context of multiple receive chains.
Communication receivers typically include a receive chain that comprises a front-end circuit providing initial signal conditioning and amplification of an antenna-received signal. Such front-end circuits vary in detail depending on the nature of the received signals and the particular implementation of the associated communication receiver, but most receivers implement some form of automatic gain control (AGC) for such front-end circuits.
With AGC, the gain (or gains) of the front-end circuit is varied responsive to changing received signal strength, which itself is subject to rapid changes due to changing fading and interference conditions. The overriding goal of AGC is to maintain the received signal in a useful amplitude range, while avoiding a saturation condition in any of the receive chain circuitry. For example, assuming that the received signal as output from the front-end circuit is digitized for subsequent baseband processing, AGC would be used to maintain the received signal at a reasonable amplitude relative to the input voltage range of the Analog-to-Digital Converter (ADC), without exceeding that input range.
Processing the baseband samples provided by the ADC to determine received signal strength (or power) provides a mechanism for generating AGC commands. Because of the need to maintain the rapidly changing received signal within an appropriate signal range, e.g., properly scaled relative to the dynamic range of the ADC and within the voltage limits of the receive chain amplifiers, etc., such baseband processing typically is carried out at a high rate. Although AGC processing may be carried out in software, dedicated hardware oftentimes is used to support the high processing rates.
In either case, the performance capabilities of the baseband circuit tasked with supporting the AGC function must be commensurate with the AGC performance requirements. While meeting those requirements is practicable in receiver configurations that use a single receive chain, meeting them for multiple receive chains may be onerous. That is, implementing a separate AGC function for each one of multiple receive chains may be impractical in terms of the baseband resources consumed or the overall level of performance required (i.e., processor clock speed, power, etc.).